/Engine/Source/Runtime/Slate/Public/Widgets/Input/SMenuAnchor.h
Computes the placement geometry for menus displayed in a separately created window
[FGeometry](API\Runtime\SlateCore\Layout\FGeometry) ComputeNewWindowMenuPlacement ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & AllottedGeometry, const FVector2D & PopupDesiredSize, EMenuPlacement PlacementMode ) const